Variability of blood pressure and heart rate in borderline and mild hypertension : With special reference to spectral analysis

Sammanfattning: The aim of this thesis was to study whether blood pressure (BP) or heart rate (HR) variability in borderline (BHT) and hypertensive (HT) subjects differs from that in normotensive (NT) subjects, and whether indices for BP and HR variability can be used in risk stratification for future hypertension. The study groups consisted of 35 NT, 29 BHT, and 34 HT middle-aged men. Except for hypertension, all subjects were healthy and were never treated with any permanent medication. At baseline, electrocardiogram and intra-arterial BP were recorded by the Oxford method over a 30-hour period. By means of spectral analysis, BP and HR variability were divided into oscillatory components arising from respiration, Mayer waves, and vasomotor activity. In addition, the mechanisms underlying diurnal variation of BP were studied using stroke volume, cardiac output, and total peripheral resistance determined by a pulse contour method. The principal finding was that in BHT subjects the frequency of the Mayer waves in BP and HR was shifted to lower vales as compared with NT and HT subjects. This may be due to increased sympathetic tone. Moreover, circadian systemic hemodynamics were altered in BHT and HT subjects. During the night, strokevolume was increased in the BHT and HT groups as compared with the daytime average, but did not change in the NT group. The abnormality may reflect reduced venous capacity causing increased cardiac filling.Five years later, the subjects were reassessed using casual BP measurements. Three fourths of the BHT subjects had progressed to hypertension. In the NT and HT groups, the majority of the subjects were still in their initial classification group. The frequency of the Mayer waves at baseline was inversely correlated with the follow-up BP levels. In a logistic regression model, low frequency of the Mayer waves at night and night-time increase in stroke volume were significant predictors of progression to hypertension.In conclusion, the results suggest that there are differences in cardiovascular regulatory systems between NT, BHT, and HT subjects, and that those NT and BHT subjects who have aberrations in the regulatory systems are at increased risk of developing sustained hypertension.